Recently, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. Also, the secondary battery has attracted considerable attention as a power source for electric vehicles (EV) and hybrid electric vehicles (HEV), which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuel.
As a result, kinds of applications using the secondary battery are being increased owing to advantages of the secondary battery, and hereafter the secondary battery is expected to be applied to more applications and products than now.
Small-sized mobile devices use one or several battery cells for each device. On the other hand, middle- or large-sized devices, such as vehicles, use a middle- or large-sized battery module having a plurality of battery cells electrically connected with each other because high output and large capacity are necessary for the middle- or large-sized devices.
The size and weight of the battery module is directly related to the receiving space and output of the corresponding middle- or large-sized device. For this reason, manufacturers are trying to manufacture small-sized, light-weight battery modules. Furthermore, devices, which are subject to a large number of external impacts and vibrations, such as electric bicycles and electric vehicles, require stable electrical connection and physical coupling between components constituting the battery module. In addition, a plurality of battery cells are used to accomplish high output and large capacity, and therefore, the safety of the battery module is regarded as important.
Preferably, the middle- or large-sized battery module is manufactured with small size and small weight, if possible. For this reason, a prismatic battery or a pouch-shaped battery, which can be stacked with high integration and has a small weight to capacity ratio, is usually used as a battery cell of the middle- or large-sized battery module. Especially, much interest is currently generated in the pouch-shaped battery, including a sheathing member made of an aluminum laminate sheet, because the weight of the pouch-shaped battery is small, and the manufacturing costs of the pouch-shaped battery are low.
In spite of the above-mentioned advantages, however, the pouch-shaped battery, used as a unit cell of the battery module, has several problems.
First, the pouch-shaped battery is constructed in a structure in which the plate-shaped electrode terminals protrude from the upper end of a battery case, with the result that the electrical connection between the electrode terminals necessary for constructing a battery module is difficult. The electrical connection between the electrode terminals is accomplished generally by coupling the electrode terminals to each other by welding using wires, plates, or bus bars; however, the coupling between the plate-shaped electrode terminals by welding is not easy. Generally, the plate-shaped electrode terminals are partially bent, and the metal plates or the bus bars are welded to the bent portions of the plate-shaped electrode terminals, which requires skilled technique and complicates a process for electrically connecting the electrode terminals to each other. Furthermore, the coupled region may be separated from each other due to external impact, which causes the defect of the pouch-shaped battery.
Secondly, the pouch-shaped battery has a low mechanical strength. For this reason, additional members for maintaining stable coupling and assembly are required when a plurality of batteries are stacked to manufacture a battery module. For example, additional mounting members, such as cartridges, in each of which one or more unit batteries are mounted, are used when the pouch-shaped batteries are stacked to manufacture the battery module. The cartridges are stacked to manufacture the battery module.
Also, when a plurality of battery cells are used to construct a middle- or large-sized battery module or when a plurality of unit modules, each including a predetermined number of battery cells, are used to construct a middle- or large-sized battery module, a large number of members are needed generally to accomplish the mechanical coupling and electrical connection between the battery cells or between the unit modules, and a process for assembling the members is very complicated. Furthermore, a space necessary to couple, weld, or solder the members for the mechanical coupling and electrical connection is required; with the result that the total size of the system is increased.
In addition, when the pouch-shaped battery is applied to a device, such as a vehicle, to which external forces, such as vibrations and impacts, are continuously applied, the output of the device may be unsafe and a short circuit may occur due to the increase of the contact resistance at the electrical connection region of the pouch-shaped battery.
Consequently, there is a high necessity for a technology to apply a mounting member, such as a cartridge, that can be manufactured without difficulty, complement the low mechanical strength of the battery cell, and prevent the occurrence of a short circuit due to an external force and a technology of a coupling method that is capable of accomplishing easy assembly and high structural stability.